Compressors



y 9, 1964 1 1 mm; 3,133,695

COMPRESSORS Filed June 19, 1961 7 Sheets-Sheet 1 INVE/VTUR T F. ZIMMERN *Mh M+w F. ZIMMERN COMPRESSORS May 19, 1964 7 Sheets-Sheet 2 Filed June 19, 1961 mvE/vw INNER/V r" IVWWQO y 9, 1964 F. ZIMMERN 3,133,695

COMPRESSORS Filed June 19, 1961 7 Sheets-Sheet 3 F. Z/MM E RN MWM+W F. ZIMMERN COMPRESSORS May 19, 1964 7 Sheets-Sheet 4 Filed June 19, 1961 v F. ZI/ IMER/V 'M, WW4 [Zuni May 19, 1964 F. ZIMMERN 3,133,695

COMPRESSORS Filed June 19, 1961 7 Sheets-Sheet 5 F. Z/NNEHN W F. ZIMMERN COMPRESSORS May 19, 1964 '7 Sheets-Sheet 6 Filed June 19, 1961 FIG. 6

INVENTM F. Z/M/ /ERN May 19, 1964 F. ZIMMERN 3,133,695

COMPRESSORS Filed June 19. 1961 7 Sheets-Sheet '7 IN VE/VTOR E Z immern A TTORNE Y3 United States Patent C) ice Claims priority, appiication France June 22, 1960 13 Claims. (Cl. 230-450) It is well known that turbine type compressors may be designed which have relatively a high horsepower per unit of weight by reason of the high speeds at which they may be operated, but they do not on the other hand, permit high pressures to be obtained in a single stage, and this in the long run reduces their thermal efliciency and their efficiency per unit of weight, despite their high operating speeds.

Attempts have already been made to eliminate these disadvantages by using compressors comprising a screw having a circular pitch line (hereinafter referred to as a spherical screw) turning at high speeds between two stationary casings, the inner walls of said casings being shaped to conform to the shape of the screw. The screw cooperates with one or two pinions which mesh with said threads and are preferably positioned in alignment with each other in a diametral plane through said screw, the teeth on-said pinions serving as pistons to compress the fluid entrapped in the ends of the plurality of compression chambers constituted by the spaces between each pair of contiguous threads and one of the walls of said casing.

The compression chambers are first directly connected at one end to the low pressure region containing the fluid to be compressed, until they are blocked off from that end by the teeth of one of the pinions. They are then connected, one after the other at their other end, to a high pressure fluid receiving region, when one of the threads which defines each pressure chamber passes out of engagement with said pinions, or with the other face of one single pinion. In such compressors, the volume of each compression chamber is varied by progressively changing the height of each thread between the central part of the spherical screw, said central part being positioned at the side of the chamber containing the fluid under pressure, and the extremity of the spherical screw, which is positioned near the chamber containing the fluid which is not under pressure.

In this manner as the spherical screw turns, the volume of each of the compression chambers which is comprised between two pinions or between two faces of one single pinion progressively decreases in proportion to the axial displacement of the compression chambers between the extremity and the middle portion of the spherical screw, by reason of the progressive decrease in the height of the threads from the extremity of the screw to its central part.

This progressive reduction in volume continues until each compression chamber ceases to be blocked by the second pinion, the fluid thus compressed then passing into the high pressure chamber.

It will be readily understood that the necessity of varying the height of the threads on a spherical screw poses complex manufacturing problems, and that in any case the volume of compressed gas is compressed only transversely and not longitudinally of the lands, so that the degree of compression which may be obtained is limited.

The new compressor according to the present invention permits greater degrees of compression to be obtained because the threads of the compressor have an inclination such that at the moment at which one of the pistons blocks off one end of a given compression chamber, the other end of this compression chamber is already clear of the other pinion and cooperates with a base plate which blocks its lower end until the base of the said compression 3,133,695 Patented May 19, 1964 chamber approaches the first pinion and comes into communication with the outlet in said base plate.

It will be readily understood that the improvement consisting in modifying the inclination of the threads of the spherical screw so that their lower ends are closed by a base plate may also be combined with a variation in the height of the'threads, which permits a substantial increase in the degree of compression per stage, thus multiplying together the compressive efiFects resulting from each arrangement.

It is also possible to use a cylindrical screw, the pinions being in this case replaced by racks meshing with the screw threads and consisting of a plurality of pivotally connected elements joined together to form endless chains, so as to permit continuous rotation about two cogwheels, the return section of these chains being parallel to the section which meshes with the screw.

It is possible to seal the various compression chambers oil from one another, along the casing wall and along the base plate, by suitable means, but the use of solid sealing means, the defects of which are well known, especially in the case of piston type compressors, leads to frictional contacts requiring lubrication, and this is difiicult to provide because of oxidation of the lubricant. Such frictional contacts also limit the maximum speed of rotation which can be obtained, and consequently the output of the device per unit of weight.

In a preferred embodiment of the invention, these solid seals are replaced by liquid seals, which, by reason of the great speed with which heat is exchanged between the liquids and the metallic surfaces in contact with the gas being compressed or expanded, also serves to cool the metallic surfaces being heated by that gas, even though the gas may be at a relatively high temperature, as for example in the case of an internal combustion engine. This permits the elimination of all the sealing problems which, in other constructions, result from expansion of the said metallic surfaces.

These liquid seals provide an almost perfect sealing, since near the leakage zones the presence of a stream of liquid suflices to prevent the escape of gas, because the liquid has a much higher viscosity and inertia.

Other characteristics of the present invention will be more clearly understood from a reading of the following description of three embodiments of the compressor according to the present invention, one of which uses liquid seals, these embodiments being described purely by way of example, and in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic perspective view of a compressor assembly according to the invention comprising a spherical screw made in three parts assembled on the same shaft;

FIG. 2 is an axial section of a spherical screw such as that of FIG. 1, taken through the central plane of the pinions which cooperate with said spherical screw;

FIG. 3 is a horizontal section through the same device, taken along the line III-III of FIG. 2;

FIG. 4 is a schematic view of a second embodiment of the compressor, comprising a cylindrical screw made in one piece, which cooperates with racks which consist of chains of articulated elements;

FIG. 5 is a schematic perspective View of a third embodiment of the spherical screw compressor, provided with liquid seals adjacent the pinions which cooperate with the threads of the said spherical screw;

FIG. 6 is a developmental schematic view showing how the said liquid seals provide a fluid tight seal between the spherical screw and the pinions which serve as racks, and also provide a fluid tight seal between the crests of the threads of said screw and the casing walls which abut these crests; and

FIG. 7 is a schematic elevational view of a compressor corresponding to the embodiment of FIGS. 5 and 6, and showing the means for recycling the liquid of said liquid seals.

FIG. 1 is a schematic view illustrating the operation of the apparatus, in which the spherical screw, the upper part of which is designated by reference numeral 1, is turned by the shaft 2., which extends through the screw from one end thereof to the other. The air enters as indicated by the arrows 3, and first fills the spaces between the forward part of the spherical screw and the casing 4 which encircles it, moving to the left as the screw turns in the direction indicated by the arrow 5.

From the moment at which one tooth 6 of the pinion 7 is in position between two adjacent threads 8 and 9 of the spherical screw, the air which enters freely between the two threads 8 and 9 is progressively compressed by the tooth 6, which acts as a piston, until the moment at which the base of the lower thread 9 passes the position occupied by the thread 10, thus connecting the space between the threads 8 and 9 with the outlet 11 shown at the right of FIG. 1.

It will be seen that this outlet is provided with a bevelled edge 12 which permits all the air in the compression chamber to be evacuated at the moment at which the thread 8 in its turn passes by the outlet 11, the compressed air then leaving in the direction of the arrow 13.

The compression chambers are closed at their bottoms by the base plate 14.

It will be readily understood that the rotation of the shaft 2 and the spherical screw 1 in the direction of the arrow '5 drives the two pinions provided in the embodiment shown on FIG. 1 in the direction of the arrows 15. The clearance between the crests of the threads of the spherical screw 1 and the two casing halves 4 and 4a on opposite sides of the pinions 7, is sealed by providing a spiral sealing member shown by the black lines 16 along the crests of said threads.

In order to prevent these sealing members from being displaced toward the bottom so as to rub against the base plate, they are fixed in place at the upper end of the screw by drops of solder, as shown at 17.

The use of casing halves having inner surfaces which are graphited or coated with a layer of solid lubricant which withstands the operating temperatures of the apparatus, might permit the elimination of said sealing members.

The pinions 7 are held in engagement with the spherical screw by means of two shafts 18, which are slightly eccentric at the bottom so as to prevent the pinions from moving away from the screw as a consequence of the differences between the pressures exerted by the compressed fiuids on these pinions at points thereon which are symmetrically positioned with respect to their axes of rotation.

The spaces 19 between these axes 18 and the lower part of the pinions 7 also permit the lubrication of said pinions.

In this connection it should be noted that the embodiment comprising a spherical screw, the pitch of the threads varies progressively and continuously from the center of the spherical screw toward its upper and lower ends.

It should also be noted that the section of the teeth of the pinions is determined by taking this feature into account, so that the teeth which mesh with the flanks of the threads of the screw have one transverse section at the level of the central part of the screw and a different transverse section, corresponding to a distortion of the teeth of the pinion, at the level of the upper and lower parts of the spherical screw, the close meshing which ensures a fluid tight seal between the different compression chambers at the level of a pinion being always assured at the flanks of threads of the spherical screw, at

least along the line connecting said transverse sections at the level of the two intermediate parts of the spherical screw, that is to say, between the said median part and the said two end parts.

'FIG. 2, independently of the paths followed by the lubricating oil, especially through the passages 20 and 21, shows a specific method of constructing the apparatus, particularly with respect .to the shape of the base 14 and the screw 1.

The latter consists in fact of several parts assembled when the compressor is built, and then fixed together by means of connecting bolts 22 and a member 23 the upper part of which carries a sealing ring 24, of self-lubricating plastic for example, surmounted by a socket 25 encircling the lubricating hole 20.

Nuts and lock nuts 26 hold the upper part 27 of a ball bearing race 28, also keyed to the member 23, the entire assembly rotating with respect to the casing 29 of the stator on roller bearings 30.

A shaft 14 is provided at the lower end of the screw. The screw is driven through this shaft which is fixed to the various sections of the latter by means of the projections 32 and a nut 33, which holds an assembling cone 34 below the various sections of the screw, a nut 35 and lock-nut 36 being also provided at the lower end to hold the lower half 37 of a ball bearing race 38- at the lower side of the base plate 41, while ball bearings 39 permit the screw assembly to rotate easily with respect to the base plate 14.

The casing halves are indicated at 41 and fixed to each other by the cover 29. The profile along which they intersect with the recesses which receive the pinions is shown at 40.

The ring 25, which serves as a bearing, is held in place on the stator by arms 42 connected to the plate 29 through a reinforcing plate 43 attached to the plate 29 by four bolts 44 shown on FIG. 2.

The plate 29 is itself fixed to the said casing halves by bolts spaced about the periphery of said plate.

Circular sealing rings 45 seal the clearance space between the plate 14 and the lower part of the screw.

The shafts 18 are mounted inside casings 46 filled with lubricating oil and visible on FIG. 3. These casings are in communication with those (49) which encircle the casing halves 4, and the oil in the casings 49 cools the outer part, whereas at the level of the casings 46, it penetrates between the teeth of the individual pinion segments 7a to 7d which make up each pinion, so as to lubricate the teeth of these pinion segments.

FIG. 3 is a section through the apparatus taken along the central horizontal plane of the screw, and shows the three projections 32 used to assemble the three-parts of the screw 1.

The casings 46 serve to mount and permit lubrication of the shafts 18 and carry ball bearings 47 in which the shafts 18 are free to rotate when the pinions are driven by rotation of the screw. These pinions are themselves axially supported between roller bearings 48 which permit the pinions to turn without excessive friction between them and the casings which support them in their proper positions.

The casings 46 are fixed by any suitable means to the two outer casing halves 49, which encircle the two inner casing halves. Passageways 50 admit lubricating oil to cool the outer surfaces of the inner casing halves. This oil then flows out toward a heat exchanger through the passages schematically indicated at 51 on FIG. 3.

The shafts 18 bear directly on the insides of the individual pinions 7a and 7b, and are turned by them. These pinions are thus rigidly spaced at a predetermined distance from the screw so as to permit expansion of the various parts.

In order that the individual pinions 7c and 7d may bear sufficiently tightly on the bottoms and tops of the threads to adequately ensure against leakage, while per-' mitting the necessary play for expansion, and independently of the means for preventing leakage along the flanks of the threads, a roller bearing 52 (shown at the left of FIG. 3) is provided, and cooperates with an elastic sleeve 53.

By reason of the eccentricity of the axes 18, this sleeve is constantly under compression and biasses the pinions 7c and 7d through said roller bearings, against the tops and bottoms of the threads, in the same manner as a piston ring is elastically biased against the inner wall of the cylinder in which it moves.

FIG. 3 shows the orifices 21 of the lubricating passages, already shown on FIG. 2, as well as the outlets 21a of the passageways, through which the oil passes to the lower part of the screw through pipes 21b shown on FIG. 2.

The screw 1 may be assembled in three parts on the drive shaft 31 of the compressor. This assembly is made by means of the projections 32 which fit into recesses 32a.

Assembling bolts 22 connect the member 23 to the three sections of the screw 1 and screw into tapped holes 22a.

The shaft 31 is also provided with a threaded portion 33a which carries the nut 33 and a threaded portion 35a for the lock-nut 36.

FIG. 4 shows a slightly different embodiment in which the spherical screw is replaced by a cylindrical screw 112.

Because of this cylindrical form, the pinions '7 consist of a plurality of rack-like elements 7a which are articulated to each other.

The rotation of the screw 1b tends to impart to the rack like elements a translational movement in the direction of the arrows 15a.

Moreover, the rotation of the pulleys or wheels 54, which cooperate with the backs of the articulated elements 7a, while slower than the rotation of the shaft 2 engenders strong centrifugal forces tending to separate the articulated members 7a.

This is why the pivotal axes 55 of the various rack-like members carry rollers 56 which project beyond the sides of the rack proper and frictionally engage a ramp 57 which extends around the pulleys 54. The ramp 57 also extends along the side of the endless chain which is furthest from the screw 1b.

In this way, the centrifugal force tends to press the rollers 56 against the ramp 57, thus avoiding any abnormal force tending to separate the segments of the endless chain.

At the side of the rack nearest the screw 1b are springs 58 which bias a member 59 which presses the segmental rack chain against the screw 1b.

Despite the difiiculty of making racks capable of meshing with a cylindrical screw, this device offers several advantages, particularly in the case of liquid pumps turning at relatively low speeds.

In the first place, the cylindrical screw can be made in one piece, and need not be assembled from several component pieces as in the case of the spherical screw.

It will be readily understood that, in the case of the spherical screw, its shape does not always permit the teeth of the pinions to be placed directly in mesh between the corresponding threads of the spherical screw, and it is necessary to progressively turn these pinions while imparting a rotational movement to one of the segments of the screw 1, until a pinion reaches the edge of this segment, a second segment being then assembled onto the corresponding projection 32 of the drive shaft 31 of the screw, so as this shaft is turned further, the first pinion may be meshed with the second screw segment and the second pinion with the first segment, the third screw segment being then assembled in the same manner when the first pinion reaches the edge of the second segment, the assembly cone for the lower part and the upper assembly plate being put in place at the same time and bolted by means of bolts 22 and nut 33.

Moreover, it is no longer necessary, in order to insure proper sealing along the teeth of the screw, to resort to a specially designed tooth shape for the pinions. This scaling is improved in the case of a cylindrical screw because it always takes place between the teeth of the worm and rack along an entire surface, and not, at certain times, merely along an edge as in the case of the spherical screw.

Finally, in the case of incompressible fluids, the volume of the space between the two adjacent screw threads and two mating pinions does not vary during the rotation of the screw, and this is advantageous.

The direction of rotation of the screw may also be changed, together with that of the ramps of the sealing means between the screw and the base plate, when the device must function as an expansion device for mechanical or refrigerating purposes.

FIG. 5 shows the adjacent threads 8 and g of the spherical screw of FIG. 1, the base plate 14 with its outlet 11 and the two casings 4 and 4a, as well as the drive shaft 2, and the arrow 5 indicating the direction in which the screw turns.

A nozzle 60 connected to a recycling device, which will be described in detail in connection with PEG. 7 permits a liquid such as water, for example, to be injected at a suitable speed, in order to insure the formation of a stream of liquid having a cross-section equal to that of the base of the nozzle and running at an average linear speed corresponding to that of the part of pinion '7 which is in contact therewith.

It is easy to understand that this stream of liquid occupies the radial space between the bottom of the teeth 8 and 9 of the spherical screw and the casing 4, which is shown partially broken away in order to show the operation of the liquid seal more clearly.

When the spherical screw turns in the direction of the arrow 5, the liquid 61 flows at a speed corresponding to the speed of rotation of the pinion 7, this stream of liquid thus constituting the equivalent of a second liquid pinion laminated against the pinion '7 by the pressure of the gases tending to escape between the worm and the pinion 7.

The leakage of compressed gas is thus prevented and it is the liquid which escapes through the clearance space between the pinion and the screw, regardless of whether this clearance results from imperfect manufacture or mere wear.

in any case, the flow of liquid through these clearances is restricted by inertia and the viscosity of the liquid, so that the device is almost perfectly sealed.

In the case of an expansion device, the arrangement would be reversed, and the liquid stream would come in on the same side as the gas to be expanded.

It should be noted that the device shown on FIG. 5 is useful, regardless of the final pressure or the initial pressure of the gas to be expanded, and the thickness of the stream of water may nevertheless be varied as a function of that pressure, so as to insure sealing in each case at the places where leakage tends to occur and take into account the tendency for these leaks to increase when the pressure increases.

Moreover, independently of the importance of leaks at difierent pressures, it is possible by adjusting the thickness of the stream of liquid, to more or less reduce the residual volume of a specific compression chamber, at the moment at which this chamber is brought into communication with the outlet for the compressed gas, so that the degree of final compression may be varied, or, in the case of an expansion device, the initial pressure of the gas to be expanded.

It should be also noted that the presence of a liquid seal at the leakage points permits all solid contact between the screw and pinions to be avoided.

In particular, if the liquid utilized is water, the pinions may consist of a rigid metallic support covered with a synthetic material such as the one commercially known as Celeron, for example. This material may be perfectly lubricated with water and, since it is completely covered by liquid, it is screened from all contact with the hot gases, which touch only the spherical screw and casings.

The use of pinions meshing with the teeth of a metallic screw may permit the use of very high linear speeds, thus improving the output of the device per unit of weight.

FIG. 6 shows the teeth of the screw and especially the adjacent teeth 8a and 9a, the screw being shown in development to facilitate an understanding of the construction. From this view it may be seen that the pressure exerted by the compressed gases drives the sealing liquid on the opposite sides of the tooth 8a in the direction of the arrows 62.

This water, driven along the threads of the screw passes through the clearances between the spherical screw and the pinions 7, and is projected by centrifugal force against the walls of the casings 4 where it forms a seal between the crests of the threads and the walls of the casings 4.

It should be noted that the streams of liquid which flow along the threads of the spherical screw in the direction indicated by the arrow 5, are subjected to the pressure of the compressed gas, which tends to force this liquid through the clearances between the casing and the screw, toward the regions in which the gas is at a lower pressure, that is to say, toward the upper compression chambers, the liquid which thus leaks through being recovered in the next compression chamber.

In practice, at the end of several seconds of operation, all the threads of the screw are covered by a film of liquid which forms an effective seal between the various compression chambers, said liquid accumulating at the base of each thread until it can pass out through the outlet for the compressed gases.

It should be noted that, in addition to forming a seal between the threads of the screw and the inner walls of the casings 4, the liquid film also cools said casings, thus supplementing the action of the conventional external cooling means which are usually carried by the compressor.

So far as the leakage between the screw and the lower base plate below the threads of the screw is concerned, it is easy to understand that the said accumulation of liquid at 63 provides a seal preventing the leakage of gas, the liquid which passes from a compression chamber into a contiguous chamber at a level above the base plate being thus collected in the contiguous chamber.

If we now consider the leakage flows along the pinions where they intersect the base plate, inside the passages provided in said base plate for the two pinions 7, they collect in the casings protecting said pinions. the rotation of which recycles the liquid toward the upper part of the device.

FIG. 7 illustrates the overall mechanism for recycling the liquid which escapes through the outlets 11 and how this Water is separated from the compressed gas.

The mixture of compressed gas and liquid which comes in through the nozzles 60 is, as has already been mentioned, expelled through the outlets 11, from which the liquid falls under the influence of gravity to the bottom of a reservoir 64, while the compressed gas escapes through the orifice 65.

It is quite clear that it is possible to improve the separaration between the gas and liquid by using a known process, such as centrifuging, for example. It is easy to do this by mounting a centrifuge on the compressor shaft.

The liquid, under pressure from the gas in the sump 64 fiows out progressively through the passages schematically represented at 66 and returns to the nozzles 60, after passing through a cooler 67 also shown schematically on FIG. 7.

Valves 68 permit the supply of liquid flowing to the nozzles 60 to be regulated.

It is also possible to use the pressure of the liquid leaving the cooler 67 to fill through a branch pipe 69, a

7 l l i 8 counter-pressure chamber 70, which reduces the axial pressure exerted by the screw, thus relieving the bearings.

It should be noted that the recycling device schematically illustrated on FIG. 7 is self-priming.

When at rest, the liquid remains in the low part 71 of the sump 64, but when the compressor is started up, the pressure created, despite the leakage of gas which occurs before the liquid can provide a complete seal, suffices to initiate the circulation of liquid to the nozzles 60, thus tending to very rapidly reduce the leakage of gas and increase the pressure until the liquid circulates at its normal volume of flow.

It will be appreciated that the embodiments described may be altered, improved, or added to, and certain elements thereof, replaced by their mechanical equivalents without thereby departing from the principle of the invention as defined by the following claims.

What is claimed is:

l. A device for changing the volume of a gas, said device comprising in combination a drive shaft, an hour glass screw mounted on said drive shaft, a plurality of discrete threads on said screw, each extending from one end to the other thereof, casing means encircling said screw, the inner wall of said casing means cooperating with the crests of said threads to form with each pair of adjacent threads a compression chamber for said gas, a relatively fixed transverse plate in sealing engagement with one end of said screw, a high pressure outlet from said compressor at the same end of said screw as said plate and a low pressure inlet to said compressor at the opposite end of said screw, at least one rotatable toothed worm gear driven by said screw and having a plurality of its teeth simultaneously in engagement between the threads of said screw, in which position they blockoif from said low pressure inlet those portions of said compression chambers which lie between said plate and the teeth on said worm gear, said plate being provided with an orifice adjacent said worm gear communicating with said high pressure outlet and positioned to register exclusively with the adjacent end of each one of said compression chambers successively as said screw rotates, said plate blocking off from said high pressure outlet all of the compression chambers except the one having its end in registration with said orifice.

2. A device as claimed in claim 1 in which the threads of said screw have a circular pitch line in an axial plane.

3. A device as claimed in claim 1 in which the crests of the screw threads carry sealing means soldered to the end of said screw adjacent said low pressure inlet.

4. A device as claimed in claim 1 in which there are at least two worm gears and a plurality of discrete threads for each gear, each thread extending from one end of said screw to the other while extending over a fraction of the circumference of said screw substantially equal to the reciprocal of the number of worm gears.

5. A device as claimed in claim 1 comprising means for lubricating the worm gears and screw threads, and cooling said casing, said means utilizing the centrifugal force exerted by rotation of said screw to circulate a cooling liquid.

6. A device as claimed in claim 5 comprising liquid seals formed by a circulating liquid, said seals covering said pinions and sealing the clearances between said screw threads and easing with a stream of liquid which is supplied to said casing at the same speed as that at which said worm gears rotate, and means for injecting said liquid at the same side as that upon which the gas enters, said liquid serving to cool as well as lubricate the surfaces with which it comes in contact.

7. Device as claimed in claim 6 in which the worm gears are provided with a metallic sheathing coated with a synthetic material of a type suitable for lubrication by said liquid.

8. Device as claimed in claim 6 in which the worm 9 gears are mounted in individual casings connected to the screw casing and through Which the leakage of liquid between said Worm gears, said casings and said transverse baseplate can be recycled.

9. Device as claimed in claim 6 comprising a centrifuge at the outlet end of the device, said centrifuge serving to separate said gas from said liquid.

10. Device as claimed in claim 6, comprising nozzles for injecting said liquid into said screw and regulating means for regulating its flow through said nozzles in proportion to the maximum fluid pressure in said device.

11. Device as claimed in claim 8 comprising a circuit through which said liquid is recycled to said nozzle, and a counter-pressure chamber supplied from said circuit.

12. Device as claimed in claim 8 comprising means for regulating the thickness of the liquid seals so as to regulate the final degree of compression attained by the device.

13. Device as claimed in claim 12 in which the said regulating means is controlled by apparatus which simultaneously controls the driving motor of the screw, so as to maintain the speed of rotation of the screw constant regardless of the degree of compression selected.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A DEVICE FOR CHANGING THE VOLUME OF A GAS, SAID DEVICE COMPRISING IN COMBINATION A DRIVE SHAFT, AN HOUR GLASS SCREW MOUNTED ON SAID DRIVE SHAFT, A PLURALITY OF DISCRETE THREADS ON SAID SCREW, EACH EXTENDING FROM ONE END TO THE OTHER THEREOF, CASING MEANS ENCIRCLING SAID SCREW, THE INNER WALL OF SAID CASING MEANS COOPERATING WITH THE CRESTS OF SAID THREADS TO FORM WITH EACH PAIR OF ADJACENT THREADS A COMPRESSION CHAMBER FOR SAID GAS, A RELATIVELY FIXED TRANSVERSE PLATE IN SEALING ENGAGEMENT WITH ONE END OF SAID SCREW, A HIGH PRESSURE OUTLET FROM SAID COMPRESSOR AT THE SAME END OF SAID SCREW AS SAID PLATE AND A LOW PRESSURE INLET TO SAID COMPRESSOR AT THE OPPOSITE END OF SAID SCREW, AT LEAST ONE ROTATABLE TOOTHED WORM GEAR DRIVEN BY SAID SCREW AND HAVING A PLURALITY OF ITS TEETH SIMULTANEOUSLY IN ENGAGEMENT BETWEEN THE THREADS OF SAID SCREW, IN WHICH POSITION THEY BLOCK OFF FROM SAID LOW PRESSURE INLET THOSE PORTIONS OF SAID COMPRESSION CHAMBERS WHICH LIE BETWEEN SAID PLATE AND THE TEETH ON SAID WORM GEAR, SAID PLATE BEING PROVIDED WITH AN ORIFICE ADJACENT SAID WORM GEAR COMMUNICATING WITH SAID HIGH PRESSURE OUTLET AND POSITIONED TO REGISTER EXCLUSIVELY WITH THE ADJACENT END OF EACH ONE OF SAID COMPRESSION CHAMBERS SUCCESSIVELY AS SAID SCREW ROTATES, SAID PLATE BLOCKING OFF FROM SAID HIGH PRESSURE OUTLET ALL OF THE COMPRESSION CHAMBERS EXCEPT THE ONE HAVING ITS END IN REGISTRATION WITH SAID ORIFICE. 